Magnetic pole



Aug. 12, 1952 R. L. JAESCHKE MAGNETIC POLE 2 SHEETS-SHEET 1 Filed Nov.1, 1950 Aug. 12, 1952 R. JAESCHKE 2,606,948

MAGNETIC POLE Filed Nov. 1, 1950 2 SHEETS-SHEET 2 TORQUE Patented Aug.12, I 1952 MAGNETIC I POLE Ralph L. Jaeschke, Kenosha, Wis., assignor toDynamatic Corporation, Kenosha, Wis., a corporation of DelawareApplication November 1, 1950, Serial No. 193,417

This invention relates to magnetic poles for eddy-current dynamoelectricmachines, including clutches, brakes, dynamometers and the like. Theinvention is an improvement upon apparatus such as shown in Patent2,470,596.

Among the several objects of the invention are to produce an efiicientlow-cost field member par ticularly for use in small-sizeddynamoelectric machines, although the invention is not limited to thisclass of apparatus.

Briefly, the invention comp-rises pole spiders having interdigitatedpolar teeth which are primarily stamped and cold pressed from heavyferrous (steel or iron) sheets. The shapes of the spiders are adaptedfor minimum flux leakage between poles, minimum magneto-motive forcerequired to force magnetic flux across the air gap, and minimum magneticpull-over during operation, without loss of efficiency of coupling andwithout the introduction of undue complications in stamping and formingthe spiders. Other objects will be in part apparent and in part pointedout hereinafter.

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

Fig. 1 is a longitudinal section of a slip clutch embodying one form ofthe invention;

Fig. 2 is a cross section taken on line 22 of Fig. l, but showing thefield member only;

Fig. 3 is a developed view of certain pole faces viewed on line 3-3 ofFig. 1;

Fig. 4 is a perspective view of the field member of Fig. I removed fromthe machine;

Bracketed Fig. 5 shows at the bottom of the bracket a fragmentary crosssection of an alternative form of the invention and at the top aprojected view of the corresponding pole face;

Bracketed Fig. 6 shows at the bottom of the bracket a fragmentary crosssection of another form of the invention and at the top a projected viewof the corresponding pole face;

spondingparts throughout the several views of the-drawings.

3 Claims. (Cl. 172-284) Referring now more particularly to Fig. 1, thereis shown at numeral I a drive shaft supported upon bearings 3 andlocated within a driven quill 5. It is to be understood that the drivingand driven relationship between members I and 5 may be reversed, thisconstituting a simple inversion. The driven quill 5 supports an inductormember 1, which includes a magnetizable ferrous (iron or steel) drumportion 9 in which eddy currents may fiow.

The shaft I carries a field member shown generally at II. This comprisesa magnetizable (iron or steel) sleeve l3 around which is wound anannular field coil I5, flanked by two magnetizable (iron or steel)spiders I1 and [9. These are welded to the sleeve I3. The spiders I1 andH! are composed of pole rings 2| and 23, respectively, welded to-thesleeve I3. Extending from the pole rings 2| and 23 are interdigitatedpolar teeth 25 and 21, respectively.

The spiders l1 and I9 are, for example, stamped from flat heavy steelsheets, say /2-inch thick for a field member 5 inches in diameter. Afterstamping the teeth '25, or 27 as the case may be, are bent by a formingoperation in a press. The teeth are then trimmed on their sides to theshapes explained below. After assembly on the sleeve I3 and around thecoil I5, which assembly interdigitates teeth 25 and 21, the outer endsof the teeth 25 and 21 are cylindrically machined so as to provide asmall air gap 29 between the field member II and the inductor drum 9.This gap should be as small as possible and is, for example, .020 inch.The smaller the gap is, the less magneto-motive force is required toforce flux across it, but the more damaging any usual magnetic pull-overeifect- (due to slight eccentricity) has between the field member I land the inductor 9. It is therefore important that the pull-over effectbe minimized.

Current is supplied to the coil I5 through a collector ring 3I, thecircuit being completed through a grounding collector ring 33. When thecoil I5 is excited, a toroidal flux field such as shown at F isproduced, which loops the coil I5, passing through the sleeve I3 and,for example, out through ring 2|, teeth 25 (which become north), acrossgap 29 into drum 9 thence back through the gap 29 into teeth 21 (whichbecome south), returning to the sleeve [3. If the shaft I be thendriven, the resulting north and south poles constituted by the teeth 25and 21 sweep through the inductor 9, causing eddy currents therein whichgenerate a reactive magnetic field, causing a driving action between thefield II and pole faces 59 appear as symmetrical quadrilate,

erals (Fig. 3). Being oppositely related, adjacent edges 31 areparallel. This bevel feature also prevents interference between thepoles and 21 when the spiders 2i and 23 are brought into positionflanking the coil l5.

As indicated in Fig. 1, an exemplaryangle of 4 from more complex onesfor arriving at any comparable results which, however, require that thefield spiders comparable to I! and H) be cast in order to produce theproper pole shapes. An advantage of the present invention is that thesimple spider stamped and pressed from flat stock may be used to obtainthe desired results, particularly in smaller machines, without-thenecessity for costly machining operations-toduplicate the more complexshapes usually obtained by casting. However, it is possible to cast thespiders of the present invention if desired.

In Fig. 5 is shown a form of the invention in which a bending angle isemployed for the bending of the poles is 45 with respect to a planenormal to the axis of shaft I. stood that bending operations of thisnature are more or less accurate-,depending upon the working qualitiesof the iron or steel used and the character of the press, so that insome instances the appearance of t the poles may be slightly curved asshownin Fig. '7, wherein like numerals designate like parts, the poleteeth havin been renumbered 25A and 21A. They are still bent essentiallyata 45 angle. t t

- By means of the above-described very easily made field structure flowseveral important advantages: first, the teeth 25 and 21, being tiltedtoward one another and overlapping, cause a tilt in the positions of theintervening V-shaped and beveled notches 35. This in the case of eachspider l1 and I9 produces very large open spaces above the coil andbetween the teeth on a given spider, wherein there is nothing but airand no magnetic material. digitating region (triangular in crosssection) of the pole faces 59 (Fig. 1) does the material of one set ofpoles .in-fill the notches between the other set of poles. The result isan extreme reduction of cross leakage of flux between the poles.

Moreover, the V-shaped notches 35, the bevels :11 and the peripheralmachining cause the poles 2'5 and 21 to taper down in cross sectionproceeding from the respective pole ring 2| or 23. This .taper is ofsuch an amount that proceeding from a pole ring to the point where theytriangularly overlap (see plane P), successive sections carry n.substantially constant flux density cross leakme of flux being takeninto account. On the ther hand, beyond plane P at the overlap thewrpendicular cross sections on a pole increase s presented to the fluxas it curves into the iniuctor 9, even though the poles taper down atthis point in what may be called a chisel shape. Thus by the process ofmachining the pole ends to the chisel-shapes, the flux density acrossany pole face 59 is less than the constant value through allotherfsections. This accomplishes two desirable results: fast, reductionin magneto-motive force required to force the flux across the gap 29;and second, the magneticattraction across the gap is less, thus reducingthe pull-over force. This is in combination with the saving in weightaccomplished by the' tapering of the flat teeth from the pole ringswhich works every other section of the tooth at aconstant'fiux density.The result'is that fewer ampere turns may be used in the coil I5 for theproduction of the flux at a given capacity, and a much smaller gap 29may be employed without rubbing caused by magnetic pull-over effects.

The present structure is to be distinguished It will be under-y Only inthe limited inter- Around this is lo- 213 and 23B from-which extend thebent tapering polar teeth 25B and 21B, overlapping in the triangularportion, as shown at 39, and having the pole faces 4|. In this case thepole angle from a "plane normal to the axis is 3.09. other things beingequal, results in ,a smaller area of the faces ,but'it is'still Iarger-than the cross-sectional area of lthe normal.planeQP through the pole'25B,':-thu's resulting in a 'flux density through the pole-faces whichisl'less than that through any other section of the pole. The plane P inFig. 5 has the same" significance asinFig.l. U

In Fig. 6 is shown another form ofv the in vention in whichI3C.represents the sleeve upon which a wider coil is wound. The coil isflanked by pole rings 23C and 210 from which extend the bent flat poles25C and 210. In this case the poles are bent in a angle in a planenormal to the axis. The result is a pole face .43.

In this case the pole end 'area 43 is substantially larger than thecross section of the respective pole in plane P. I e

Fig. 8 is a chart of torque transmitted, plotted against the slip speedbetween the members 9 and II. The middle curve A is characteristic-ofthe construction shown in Figs.1-4;. the'curve B is characteristic-ofthe construction shown in Fig. 5; and curve C is characteristic of theconstruction shown in Fig. 6. The conclusion to be drawnfro m Fig. 8 isthat the 45? angle used'in connection with the Fig. 1 constructionproduces the flattesttorque-speed curve after the knee of the curv'ehasbeen passed; the 30 angle results in a rising torque-speed curveafter the knee of the curve has been passed, but the knee is lower; andthe 60. angle results in a falling torque-speed curve i after the ,kneeof the curve has been passed, but the knee is higher; These curvesillustrate the: fact that the ratio of the pole end area to the minimumright section at 1? controls the torque-speed. characteristics. Theexplanation of this is that in the case of the small 30? angle of Fig;5,'the resulting small .polelend area producesthe greatestfiux-densityIt is to be observed that in noevent, inorder to obtain the improvementsspecifiedherein, is

the stated angle to be or of that orden-which would bring the polesflush down on 5 of the coil. The limits of 30 to 60 illustrated arethose that cover practical cases.

It will be observed that if any of the pole rings shown in Figs. 1, 5and 6 be separated further than shown, the pole end areas will becomestaggered. The result of such a construction would be a reduction in thetorque at low speeds, as illustrated by the dotted curve shown in Fig.8. This is mentioned to show that the construction can be adjusted tocases where a less sharp knee is desired in the torque-speed curve.

Certain definitive features of the invention are as follows: The centralportions of the spiders l7 and IE! form end rings of rectangular crosssection adjacent the ends of the coil IS. The bent polar teeth 25 and 27are flat and lie generally within the confines of substantial cones. Theflat polar teeth taper from the end rings by reason of the triangularnotches. They are chiselshaped at their small ends and overlaptriangularly in axial section so as to present alternate pole end areaslying in an imaginary bounding cylinder around the field member. Byreason of the small overlap, inter-polar flux leakage is minimized, inView of the substantial triangular openings left between each pole endand the base portions of the interdigitating poles. Lastly the notchesflare toward the coil, thus beveling the teeth for adjacent parallelismwhen interdigitated.

It will be noted (Fig. 1, for example) that because of the bevel orchisel-shaped pole ends, the thickness T of each polar tooth is lessthan the width of face W, and this is true also for the forms shown inFigs. 5, 6 and 7. This accounts for the decrease in fiuX density acrossthe pole face in each case below what it is in the last section P of thepole and hence below what it is in any section between P and the polering 2|. Each succeeding smaller pole section starting from the ring, byreason of some flux leakage ahead of it carries less flux but the fluxdensities are approximately the same out to plane P, the tapers of theteeth brought about by the V notches being designed to attain this end.

It will be understood that although the field member I l is shown insideth inductor member 9, the invention may be carried out in a field memberwherein the coil is outside of the inductor member with the teeth suchas 25 and 27 facing inward, and that this would simply be an inversion.The point in this connection will be clear by. noting the inverted typeof construction shown in Patent 2,47 0,596.

Reference is hereby made under the provisions of Rule 78 to a relatedinvention disclosed and claimed in the U. S. patent application ofMartin P. Winther, Serial No. 192,942, for Magnetic Pole, filed October30, 1950, now Patent No. 2,603,677.

In view of the above, it will b seen that the several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. A rotary field member for eddy-current clutches and the likecomprising an annular field coil flanked by pole spiders each composedof fiat bendable ferrous stock and comprising bent poles of constantthickness but having lengthwise tapers extending from the pole rin andhaving beveled ends which interdigitate and overlap with respect to thepoles of the other spider, the tapers being of an amount to provide asubstantially constant flux density throughout successive cross sectionsof the poles normal to the direction of flux therethrough starting fromthe pole ring and up to the points of overlap, the bevels providingtriangular overlaps and cylindrically positioned pole faces, the areasof said pole faces being larger than the last section of the pole whichis not overlapped so that the flux density through the pole face is lessthan th constant flux density in said successive sections, the angles ofthe poles from a plane normal to the:5 axis of rotation being in therange from 30 to 0.

2. A rotary field member for eddy-current clutches and the likecomprisin an annular field coil flanked by pole spiders each composed ofa rectangular pole ring, angled laterally tapering poles ofsubstantially constant thickness equal to that of the ring and havingbeveled ends which interdigitate and overlap with respect to the polesof the other spider, the tapers being of an amount to provide asubstantially constant fiux density throughout successive cross sectionsof the poles normal to the direction of flux therethrough starting fromthe pole ring and up to the points of overlap, the bevels providingtriangular overlaps and cylindrically positioned pole faces, the areasof said pole faces being larger than the last section of the pole whichis not overlapped, whereby flux density through the pole face is lessthan the constant flux density in said successive sections, the anglesof the poles from a plane normal to the axis of rotation being in therange from 30 to- 60.

3. Apparatus made according to claim 2 wherein the spaces between polesfiare in the direction of the coil, whereby the pole faces becomenonrectangular but quadrilateral and have adjacent substantiallyparallel edges in said pole faces.

RALPH L. JAESCHKE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,243,318 Rawlings May 27, 19412,301,424 List Nov. 10, 1942 2,484,138 Winther Oct. 11, 1949 2,519,449Findley Aug. 22, 1950 FOREIGN PATENTS Number Country Date 527,726 GreatBritain Oct. 15, 1940

